Add runtime function for string to array conversion.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 8211ae65dba92b4771471ff6383c2e96918a98a0..9abfce3ea5ea6cc7c3649571ddeeef895f086d30 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -450,9 +450,16 @@ class Heap : public AllStatic {
   // failed.
   // Please note this does not perform a garbage collection.
   static Object* AllocateFixedArray(int length, PretenureFlag pretenure);
-  // Allocate uninitialized, non-tenured fixed array with length elements.
+  // Allocates a fixed array initialized with undefined values
   static Object* AllocateFixedArray(int length);
 
+  // Allocates an uninitialized fixed array. It must be filled by the caller.
+  //
+  // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
+  // failed.
+  // Please note this does not perform a garbage collection.
+  static Object* AllocateUninitializedFixedArray(int length);
+
   // Make a copy of src and return it. Returns
   // Failure::RetryAfterGC(requested_bytes, space) if the allocation failed.
   static Object* CopyFixedArray(FixedArray* src);